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Immediate early gene induction after neonatal hypoxia-ischemia
R M Gubits1, R E Burke, G Casey-McIntosh
1Department of Neurology, University College of Physicians and Surgeons, New York, NY 10032.
Insights
The immature brain rapidly responds to hypoxia-ischemia (H-I) by increasing immediate early gene (IEG) expression. This study shows H-I triggers multiple rapid gene response systems in developing brain cells.
Area of Science:
- Neuroscience
- Molecular Biology
- Developmental Biology
Background:
- Immediate early genes (IEGs) like FOS and JUN are crucial for cellular transcriptional responses to environmental stimuli.
- The role of IEGs in the immature brain's response to hypoxia-ischemia (H-I) remains largely unexplored.
Purpose of the Study:
- To investigate the involvement of IEG products in the immature brain's response to H-I.
- To characterize the temporal and regional gene expression patterns following H-I in developing rat brains.
Main Methods:
- Seven-day-old rat pups underwent unilateral common carotid artery ligation followed by 3 hours of hypoxia.
- RNA analysis using Northern blot hybridization was performed on various brain regions at time points from 1 to 24 hours post-H-I.
- Concentrations of nine IEG mRNAs, heat shock protein 70 (Hsp70) mRNA, and glial fibrillary acidic protein (GFAP) mRNA were quantified.
Main Results:
- Significant induction of seven out of nine IEGs (excluding TIS7 and TIS10) was observed in the ipsilateral forebrain within 1-3 hours post-H-I, with some detected up to 24 hours.
- Co-induction of multiple IEGs was a common finding in the same RNA samples.
- Hsp70 mRNA induction was localized to the ipsilateral forebrain, correlating with IEG induction, while GFAP mRNA induction occurred later (18-24 hours) in the ipsilateral forebrain.
Conclusions:
- The immature brain exhibits a robust and rapid gene expression response to H-I.
- At least three distinct rapid response systems, including IEGs, heat shock, and astrocytic responses, are activated following H-I in the developing brain.
- IEG induction appears closely linked to the initial response to H-I, while Hsp70 and GFAP induction may relate to subsequent damage and reactive processes.
Abstract:
Immediate early gene (IEG) products, such as FOS and JUN, may partially mediate the long-term transcriptional response of CNS cells to specific changes in their environment. To determine whether IEG products might be involved in the immature brain's response to hypoxia-ischemia (H-I), 7-day-old rat pups were subjected to unilateral common carotid artery ligation followed by 3 h of hypoxia (8% O2/92% N2) at 37 degrees C, which results in pathological changes only in specific regions of the hemisphere ipsilateral to ligation. Time course experiments were performed, in which animals were sacrificed between 1 and 24 h after H-I. RNAs from several brain regions were analyzed by Northern blot hybridization for their relative concentrations of nine IEG mRNAs (c-fos, c-jun, junB, TIS 1 (nur77), TIS7, TIS8 (zif268), TIS10, TIS11, and TIS21). Induction of all IEGs, except TIS7 and TIS10, was observed in ipsilateral forebrain, and, less frequently, in contralateral forebrain, at 1, 2, and 3 h post-hypoxia. In some animals, lower levels of expression were also detected at 4, 18 and 24 h. With minor exceptions, co-induction of all seven IEGs was observed in a given RNA sample. Induction of two other mRNAs, representing the heat shock and astrocytic responses, were also observed. Hsp70 mRNA levels were increased only in the brains of animals exhibiting IEG induction. However, hsp70 induction was confined to the ipsilateral forebrain, implying a more direct relationship between its expression and permanent morphological damage. GFAP mRNA induction occurred predominantly in ipsilateral forebrain samples at 18 and 24 h post-hypoxia. Levels of B-actin and ubiquitin mRNAs were relatively constant in the same RNA samples. In control experiments c-fos mRNA induction was not detected after sham ligation with hypoxia, ligation with sham hypoxia, or hypoxia alone. These results suggest that the immature brain is highly responsive to H-I at the level of gene expression, involving at least three different rapid response systems.